Updated Rakefile :preview command to new Jekyll standards

jekyll --server --auto is deprecated and has been replaced with jekyll serve(r) -w(atch)
Updated _config.yml => removed auto property, deprecated in the latest jekyll
Merge pull request #179 from kvannotten/patch-1

Updated Rakefile :preview command to new Jekyll standards
Update History.markdown
Merge branch 'jekyll-bootstrap/master'